Complete issue - IMA Fungus

Zain, Moss & El-Sheikh
ARTICLE
The structural cell membrane was contiguous with the
membrane of the septum, between the pseudophialide
and merosporangium cross-walls. Here the pseudophialide
necks were cylindrical, 1.2–1.4 µm long, ca. 1–1.1 µm
diam, with a septum delimiting the merosporangium
(Fig. 1E). Pseudophialides from which merosporangia
had been released had a flared-shape structure from the
merosporangium cell wall attached to the pseudophialide
neck; the septum and septal plug, and structure within the
pseudophialide, was shrivelled (Fig. 1J).
Merosporangia and merosporangiospores
Immature merosporangia were obovoid, whereas mature
ones were obovate. Merosporangia matured first on those
pseudophialides towards the “apex” of the sporocladium with
those on the peripheral pseudophialides the last to mature.
The merosporangia of L. pennispora were obovate, 3–4 µm
wide near the base, narrowed distally to 2.0–2.5 µm wide,
18–23 µm long, and possessed regular surface annulation
with interconnecting ridges, but lacked any rod-shaped
ornamentation (Fig. 1G).
The merosporangia were produced terminally or
subterminally and singly on the pseudophialides. A septum
formed at the apex of the pseudophialide neck delimited the
merosporangium from the pseudophialide. Merosporangia
had a three-layered wall continuous with the pseudophialide
wall. The merosporangium wall comprised an outer, 150–
200 nm thick, electron-opaque layer; a middle, 200–250
nm thick, electron-opaque layer; and an inner, 40–50 nm
thick, electron-dense layer (Fig. 1H). Each merosporangium
contained a single merosporangiospore.
The merosporangiospore was obovate, 2.3–2.5 µm diam,
with a ca. 1 µm diam papilla-like base. The merosporangiospore
had a four-layered wall: an outer, 2–5 nm thick, electrondense
layer; adpressed to the outer layer, a thick, 5–10
nm, electron-dense layer; and an innermost fourth, 90–
100 nm thick, amorphous, electron-transparent layer.
The merosporangiospore wall was contiguous with the
merosporangium wall at the distal region, and separated by
an electron-opaque layer at the base of the merosporangium.
Detachment of the merosporangia from their pseudophialides
occurred at the base of the merosporangium.
Detached merosporangia possessed a single, 3–5 µm
long, “appendage” that was attached to the base of the
merosporangium (Fig. 1I). The appendage was acicular,
unbranched, ca. 0.1 µm diam and attached to the
merosporangiospore inner cell wall layer and passed through
the septum plug to the pseudophialide. Pseudophialides from
which merosporangia had been released possessed a flared
collar-like distal region with the septum, which delimited the
pseudophialide from the merosporangium, retained at the
base of the collar (Fig. 1J).
The detachment of the merosporangium from the
pseudophialide occurred by rupture of the merosporangium
wall near the base, when the merosporangiospore wall
becomes coated with the electron-opaque layer (Fig. 1K).
When the merosporangium has been detached, a part
of the merosporangium wall remained attached to the
pseudophialide neck, as well as the septum between the
pseudophialide and merosporangium. The cytoplasmic
layer between the merosporangiospore base and the
merosporangium wall appeared as a spherical-shape
structure attached to the septal-plug.
DISCUSSION
Aerial hyphae of Linderina pennispora were investigated
previously at the ultrastructure level (Young 1969, 1970b,
Benny & Aldrich 1975). The hyphae had a two-layered wall
which comprised an outer amorphous layer and an inner
fibrillar layer (Young 1969, 1970b, Benny & Aldrich 1975).
Numerous spines were described as attached to the outer
layer of the hyphal wall (Young 1970b). Benny & Aldrich
stated that the spines were attached to the inner layer of the
wall and appeared to be covered by material from the outer
wall layer (Benny & Aldrich 1975). The results presented here
show that the surface ornamentations of the aerial hyphae
of Linderina pennispora appears rod-shaped rather than
spine-like. The ornamentation is attached to the outer layer
of the hyphal wall. It is fibrillar, electron-dense, and seem
to be derived from the same material as the outer layer.
There was no definite description for the sporangiophore in
all the previously published studies on the morphology of
the species. This study revealed that the sporangiophore
of L. pennispora arose as a lateral branch of the vegetative
hyphae. The sporangiophores are narrower in diameter
than the vegetative hyphae, and the ontogeny of the
sporangiophore and its sympodial growth are described here
for the first time, and explain the diagnostic “zigzag” form of
the sporangiophore.
Benjamin (1966) described the sporocladia of Kickxellaceae
species as the most highly developed sporiferous
branchlets in Zygomycetes. The present study provides details
of the sporocladia and their ontogeny. The sporocladium
initials are produced terminally by the sporangiophore, and,
when the sporangiophore resumes its growth, the sporocladia
are displaced laterally. The terminal sporocladium is displaced
after the formation of the merosporangia, particularly at
the late stages of merosporangia development. Benny &
Aldrich (1975) observed the surface ornamentations of
pseudophialides of L. pennispora and stated that they were
coated with fewer rod-shape surface ornamentations than
the sporocladium, and comprised a structure they termed
an “abscission vacuole”. However, Young (1974) described
a similar structure in the pseudophialides of Kickxella
alabastrina, and then termed the structure a “labyrinthiform
organelle” based on its morphology. A similar structure was
also demonstrated in the pseudophialides of Dipsacomyces
acuminosporus and Martensiomyces pterosporus (Young
1968). Benny & Aldrich (1975) suggested that this structure
was related to the abscission and dispersal mechanism of
the wet-spored species of Kickxellaceae. They believed that
this structure was produced from the septum delimiting the
merosporangium (Benny & Aldrich 1975).
Our electron microscopic studies of the pseudophialides
of Linderina pennispora show, for the first time, a concentric
arrangement of the pseudophialides on the sporocladium,
and that only the peripheral pseudophialides are coated
with a rod-shaped ornamentation. Ultra-thin sections
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ima fUNGUS